1. Field of the Invention
This invention relates generally to temperature indicators and monitors, and more particularly to a small shape memory alloy thermal exposure monitor calibrated to closely match the thermal characteristics of a perishable product and indicate whether the product has been exposed to temperatures outside of a prescribed range for an amount of time that would be detrimental to the particular product.
2. Brief Description of the Prior Art
It is of utmost importance to maintain processed produce such as food products and perishable non-food products such as medical products, drugs, research reagents, pharmaceuticals, human organs and tissues, etc., within a predetermined temperature range and to determine whether such products may have been exposed to detrimental temperatures outside the specified temperature range during some step in the chain of distribution from the source to the destination.
The demand for processed produce and perishable non-food products has pushed the limits of the distribution systems of the perishable products industry to maintain an unbroken cold chain from field to consumer and industry. Many segments of the food industry utilize a Hazard Analysis and Critical Control Point system (HACCP) which is a world-recognized, common sense approach to food safety and prevention of food contamination.
The HACCP has outlined seven principles for food safety and prevention of food contamination: (1) Conduct a hazard analysis to identify potential hazards that could occur in the food production process; (2) Identify the critical control points (CCPs)xe2x80x94those points in the process where the potential hazards could occur and can be prevented and/or controlled; (3) Establish critical limits for preventive measures associated with each CCP; (4) Monitor each CCP to ensure it stays within the limits; (5) Take corrective actions when monitoring determines a CCP is not within the established limits; (6) Keep records that document the HACCP system is monitored and working correctly; and (7) Verify that the HACCP system is working properly through tests and other measures.
Existing HACCP programs in place at the processing end of the chain are not equipped with proper tools to monitor all of the critical control points (CCP""s) in the cold chain, and temperature related problems can still occur throughout the distribution chain. Thus, there is a need for a device that can be used for economically monitoring the links in the cold chain, especially when perishable loads are broken up and re-distributed.
Temperature monitors and indicators are known in the art. There are several patents that disclose various electronic and mechanical temperature indicating devices.
Nakagawa et al, U.S. Pat. No. 4,007,637 discloses an electronic and mechanical temperature recorder which produces a continuous graphic record, scribed on a removable tape, of the temperature existing in an enclosure, such as a refrigerated railroad car, during a given period of time (e.g., the transit time of such a railroad car). This type of device is a complex mechanism and, due to its expense, would be impractical to utilize in applications where the present invention is used.
Dewaegheneire, U.S. Pat. No. 4,448,147; Weynant nee Girones, U.S. Pat. Nos. 5,018,874 and 5,335,994; and Darringer et al, U.S. Pat. No. 5,076,197 disclose xe2x80x9cstepxe2x80x9d type temperature monitors. These devices differ from the present invention in that they merely measure and indicate whether one or more temperature thresholds have been achieved. The present cumulative thermal exposure monitor, on the other hand, acts as an integrating calorimeter once a threshold temperature has been achieved, and measures heat and relates that measurement to the degree of spoilage in the product.
Manske, U.S. Pat. No. 3,954,011 discloses an example of an enzymatic color indicator of the prior art. Enzymatic color indicators are used to show the amount of temperature abuse of a stored or shipped temperature-sensitive commodity. This technology has a limited operating temperature range, is relatively expensive, and there may be a risk of interaction of the indicator solution with the products or food.
Shahinpoor, U.S. Pat. No. 5,735,607 discloses a temperature sensor having an indication surface, at least one shape memory alloy (SMA) member with a first shape at temperatures below a critical temperature and a second shape at temperatures above the critical temperature, and a plurality of indicators mounted with the members which obscure the indication surface when the members are in the first shape, and do not obscure the indication surface when the members are in their second shape. This device only indicates that a temperature threshold was exceeded, and must always be maintained at a temperature below the transformation temperature of the shape memory alloy member(s) until the beginning of the sensing operation.
The present invention is distinguished over the prior art in general, and these patents in particular by a thermal exposure monitor which has a thermally-conductive housing adapted to be placed in close proximity to a product to be monitored and at least one thermally-responsive shape memory alloy member contained in the housing having a first shape at temperatures below a critical temperature and a second shape at temperatures above the critical temperature and a transformation temperature range encompassing a prescribed detrimental temperature related to the product being monitored. An indicator associated with the thermally-responsive member is moved from an initial position as the thermally-responsive member changes from the first shape to the second shape so as to be visually observed through a window on the housing to visually indicate whether the product being monitored has been exposed to temperatures above the prescribed detrimental temperature for a period of time that would be detrimental to the product.
It is therefore an object of the present invention to provide a cumulative thermal exposure monitor that is calibrated to closely match the thermal characteristics of a perishable product being monitored.
It is another object of this invention to provide a cumulative thermal exposure monitor that monitors and indicates whether a product or container with which it is associated has been exposed to temperatures outside of a predetermined range for a period of time that would be detrimental to the product.
Another object of this invention is to provide a cumulative thermal exposure monitor that can be used with perishable food products and non-food products such as medical products, drugs, research reagents, pharmaceuticals, human organs and tissues, etc., to indicate whether such products may have been exposed to detrimental temperatures outside a specified temperature range during some step in the chain of distribution from the source to the destination.
Another object of this invention is to provide a cumulative thermal exposure monitor that has a large functional temperature range of from about xe2x88x92200xc2x0 C. to about 135xc2x0 C.
Another object of this invention is to provide a cumulative thermal exposure monitor that can be sterilized by chemicals, ionizing radiation or heat.
Another object of this invention is to provide a cumulative thermal exposure monitor that can serve as an inexpensive, convenient and effective regulatory tool for HACCP programs and allow real time decisions to be made as to the safety or quality of a perishable product.
Another object of this invention is to provide a cumulative thermal exposure monitor that may reduce liability by indicating, package by package, whether the history of a particular perishable product was within proper limits while it was in transit or storage.
A further object of this invention is to provide a cumulative thermal exposure monitor made of inert plastic and bio-compatible metal that is food-safe and has no danger of contaminating the product it is monitoring.
A still further object of this invention is to provide a cumulative thermal exposure monitor that is inexpensive to manufacture, may be disposable, and is economical to install on individual containers.
Other objects of the invention will become apparent from time to time throughout the specification and claims as hereinafter related.
The above noted objects and other objects of the invention are accomplished by a thermal exposure monitor which has a thermally-conductive housing adapted to be placed in close proximity to a product to be monitored and at least one thermally-responsive shape memory alloy member contained in the housing having a first shape at temperatures below a critical temperature and a second shape at temperatures above the critical temperature and a transformation temperature range encompassing a prescribed detrimental temperature related to the product being monitored. An indicator associated with the thermally-responsive member is moved from an initial position as the thermally-responsive member changes from the first shape to the second shape so as to be visually observed through a window on the housing to visually indicate whether the product being monitored has been exposed to temperatures above the prescribed detrimental temperature for a period of time that would be detrimental to the product.